New publications on parasites

Three new studies were published by the Caira lab in EEB that further highlight the diversity and evolution of parasites.

1. Bueno V. M.  & J. N. Caira. 2017. Redescription and molecular assessment of relationships among three species of Echeneibothrium (Rhinebothriidea: Echeneibothriidae) parasitizing the Yellownose Skate, Dipturus chilensis, in Chile. Journal of Parasitology 103: 268–284. pdf

Abstract reads: Much progress has recently been made in revising the taxonomic assignments of genera originally classified in the polyphyletic “Tetraphyllidea.” Many of these genera, including Echeneibothrium, were accommodated in the order Rhinebothriidea. However, beyond this larger taxonomic action, little work has been conducted on this genus over the past 50 yr. Consequently, the criteria used for characterizing species of Echeneibothrium have lagged behind those typically used in more modern descriptions of elasmobranch-hosted cestode taxa. A series of collecting trips to Chile to obtain cestodes from the yellownose skate, Dipturus chilensis, provided a unique opportunity to apply modern morphological and molecular methods to investigate the 3 species of Echeneibothrium reported parasitizing this skate, specifically Echeneibothrium megalosoma, Echeneibothrium multiloculatum, and Echeneibothrium williamsi. In addition to redescribing all 3 species, using morphological data from light and scanning electron microscopy, maximum likelihood and bayesian inference phylogenetic analyses of the D1–D3 regions of the 28S rDNA gene were conducted to assess their relationships among other echeneibothriids for which comparable data are available. Sequencing of 59 specimens representing these 3 species of Echeneibothrium allowed us to assess the intra- and interspecific variation in the 28S rDNA gene. The redescriptions use standardized terminology for scolex morphology, proglottid anatomy, and microthrix forms and pattern; they also expand on the original descriptions to include data on scolex size, ovary size, vas deferens and vaginal configurations, testes arrangement, and genital pore position. Our morphological work led to a major reinterpretation of the scolex morphology with the recognition that all 3 species bear an apical bothridial sucker, rather than an apical loculus, prompting emendation of the diagnosis for the family Echeneibothriidae. The presence of a band of spinitriches at the apex of the apical modification of the scolex proper seems to represent an important feature for distinguishing the 2 portions of the myzorhynchus across species. Intraspecific variation ranged from 0 to 7 bp across species and interspecific variation ranged from a low of 39–46 bp between E. williamsi and E. multiloculatum to a high of 61–66 bp between E. multiloculatum and E. megalosoma. Phylogenetic analyses indicate that the 3 species of Echeneibothrium hosted by the yellownose skate are not each other’s closest relatives, suggesting multiple colonization events of D. chilensis have occurred. Further phylogenetic investigation is also likely to confirm the status of the genus Pseudanthobothrium as a synonym of Echeneibothrium because its species generally group among members of Echeneibothrium.

2. Caira, J. N., C. J. Healy, F. P. Marques & K. Jensen. 2017. Three new genera of rhinebothriidean cestodes from stingrays in Southeast Asia. Folia parasitologica 64: 008. pdf

Abstract reads: Three genera of rhinebothriideans, previously referred to as New genus 1, New genus 2 and New genus 4, are erected in the the Anthocephaliidae. New genus 1 is established as Divaricobothrium gen. n., with Divaricobothrium tribelum sp. n. as its type species; Echeneibothrium trifidum Shipley et Hornell, 1906 is transferred to the genus as Divaricobothrium trifidum (Shipley et Hornell, 1906) comb. n. This genus is unique among rhinebothriidean genera in bearing bothridia that are posteriorly deeply divided into two lobes with facial loculi but no apical sucker, and a vagina that extends to near the anterior margin of the proglottid. Its species parasitise Indo-Pacific members of the genera Brevitrygon Last, Naylor et Manjaji-Matsumoto, Maculabatis Last, Naylor et Manjaji-Matsumoto and Pateobatis Last, Naylor et Manjaji-Matsumoto. New genus 2 is established as Barbeaucestus gen. n., with Barbeaucestus jockuschae sp. n. as its type species; Barbeaucestus ralickiae sp. n. is also described. Anthobothrium sexorchidum Williams, 1964 and Rhinebothrium shipleyi Southwell, 1912 are transferred to the genus as Barbeaucestus sexorchidus (Williams, 1964) comb. n. and Barbeaucestus shipleyi (Southwell, 1912) comb. n., respectively. This genus is unique among rhinebothriidean genera in that its bothridia are substantially wider than long, bear an apical sucker and at least one row of two or more facial loculi in their anterior half. Its species parasitise the genera Neotrygon Castelnau and Taeniura Müller et Henle. New genus 4 is established as Sungaicestus gen. n. with transfer of Rhinebothrium kinabatanganensis Healy, 2006, as Sungaicestus kinabatanganensis (Healy, 2006) comb. n., as its type species. Among the genera of its order, this genus most closely resembles Rhinebothrium Linton, 1890, however, despite the original description, the bothridia were found to bear, rather than lack, apical suckers. This monotypic genus is known only from the freshwater stingray Urogymnus polylepis (Müller et Henle). The familial diagnosis of the Anthocephaliidae Ruhnke, Caira et Cox, 2015 is emended. The family now houses five genera.

3. Gallagher K., J. N. Caira & M. Cantino. 2017. Ultrastructure of cell types within the scolex and cephalic peduncle of the litobothriidean tapeworm, Litobothrium aenigmaticum. Invertebrate Biology 136: 243–259. pdf

Abstract readsLitobothrium aenigmaticum Caira, Jensen, Waeschenbach, & Littlewood 2014 is a cestode species that parasitizes pelagic thresher sharks in Taiwan and the Gulf of California. A previous study using light microscopy suggested the scolex contains four types of unusual tissues, one of which was considered to aid in adhesion of the worm to the mucosa of the spiral intestine. The function of the other tissues was unknown. Also unknown was the function of two laterally paired ducts found extending throughout the length of the worm. The goal of the present study was to use transmission electron microscopy (TEM) to examine the internal anatomy of the scolex and cephalic peduncle of this tapeworm in more detail. Three specimens from Taiwan were examined with TEM and two with light microscopy. Transmission electron microscopy revealed that the laterally paired ducts were excretory, since they were closely associated with numerous protonephridia. The number of cell types, previously referred to as tissues, in the scolex was expanded to 11 based on a combination of features including cell size, nucleus size, ratio of the maximum diameter of the nucleus to maximum diameter of the whole cell, and types of observed organelles, as well as the presence or absence of cytoplasmic electron-dense and electron-lucent vesicles. The cytoplasm of all 11 cell types was found to include electron-dense vesicles, and all types were periodic acid-Schiff (PAS) positive. This suggests that the electron-dense vesicles may contain glycoproteins and/or mucoproteins. As all 11 cell types occurred within the region of the scolex that is surrounded by a papilla of host mucosa at the site of tapeworm attachment, we hypothesize that one or more of these cell types may produce a substance that induces this inflammatory reaction. The specific products in the secretory vesicles and how those products are released are still unclear, as are any relationships between or among the cell types in terms of products produced. Further research will be necessary to fully understand the complexity of this organism.